Food appeal and desire to eat were analyzed for the effects of food group, portion size and energy density of the foods presented as well as by participant characteristics.. Food categor
Trang 1R E S E A R C H Open Access
Assessing food appeal and desire to eat: the
effects of portion size & energy density
Kyle S Burger1,2, Marc A Cornier3, Jan Ingebrigtsen4and Susan L Johnson1*
Abstract
Background: Visual presentation of food provides considerable information such as its potential for palatability and availability, both of which can impact eating behavior
Methods: We investigated the subjective ratings for food appeal and desire to eat when exposed to food pictures
in a fed sample (n = 129) using the computer paradigm ImageRate Food appeal and desire to eat were analyzed for the effects of food group, portion size and energy density of the foods presented as well as by participant characteristics
Results: Food appeal ratings were significantly higher than those for desire to eat (57.9 ± 11.6 v 44.7 ± 18.0; p < 0.05) Body mass index was positively correlated to desire to eat (r = 0.20; p < 0.05), but not food appeal Food category analyses revealed that fruit was the highest rated food category for both appeal and desire, followed by discretionary foods Additionally, overweight individuals reported higher ratings of desire to eat large portions of food compared to smaller portions (p < 0.001), although these effects were relatively small Energy density of the foods was inversely correlated with ratings for both appeal and desire (r’s = - 0.27; p’s < 0.01)
Conclusions: Results support the hypothesis that individuals differentiate between food appeal and desire to eat foods when assessing these ratings using the same type of metric Additionally, relations among food appeal and desire to eat ratings and body mass show overweight individuals could be more responsive to visual foods cues in
a manner that contributes to obesity
Keywords: liking, wanting, food appeal, desire to eat, intake, hedonic, obesity, portion size
Background
Food intake is influenced by a number of factors such as
visual food cues in the eating environment, the hedonic
value of food and an individual’s energy state [1-3] In
today’s environment individuals are presented with
visual food cues on a continual basis Images of foods
appear in print media, on screen and are visually
pre-sented when others are eating By simply seeing food
one is aware of its availability and potential palatability,
both of which can act as incentive to initiate food intake
[4] Studies have reported that altering the visual aspects
of food, such as portion size and visibility, can increase
food intake [5-7], yet little is known about the
mechan-isms by which this occurs To understand the possible
physiologic basis of the effect of visual presentation of food, research has assessed brain activation in response
to food pictures These studies have reported that brain activation in reward and attention related areas is increased when individuals are shown pictures of energy dense, highly palatable foods [8] and that activation resulting from high calorie foods is positively associated with body mass index [8-10] However little is known about individuals’ preferences for these types of food items and their interactions with food characteristics known to influence food selection (e.g., food categories, portion size, and energy density) individual characteris-tics such as body mass and levels of dietary restraint and disinhibition
Food Liking & Wanting
A positive hedonic value of food, or food reward, is a powerful determinant of eating behavior [11] Neural
* Correspondence: Susan.Johnson@ucdenver.edu
1
Department of Pediatrics, Section of Nutrition, University of Colorado
Denver, Aurora, CO, USA
Full list of author information is available at the end of the article
© 2011 Burger et al; licensee BioMed Central Ltd This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
Trang 2responses to positive hedonic food cues occur on two
levels,‘liking’ and ‘wanting’ and have independent neural
pathways [12] While liking is commonly conceptualized
as the positive hedonic value of food and frequently
measured via visual analog scale, wanting referred to the
incentive salience and/or motivation to consume that
food item [12,13] and has been measured in a variety of
ways [14-18] Epstein and colleagues interpreted
Ber-ridge’s “motivation to consume” as the amount of work
(e.g., pushing a button) an individual would perform to
receive food [14] Wanting has also been measured by
asking a participant to choose a preferred food (between
two food items) and measuring reaction time [17]
Fin-layson and colleagues selected this ‘forced choice’
method citing that individuals may not be able to
differ-entiate between subjective liking and wanting and that
wanting could occur unconsciously [17], although this
has not been empirically tested Whereas in a repeated
measure experiment, Liem and colleagues (2009) used a
Lykert type scale after children tasted foods [18]
Further, there are few empirical data available that test
the ability to reliably assess differences in subjective
lik-ing and wantlik-ing in a similar metric in adults (for
exam-ple, visual analog scales) However, based on the
differences in these methodologies and lack of the ability
to test against a gold-standard, it is unclear if they are
measuring the same specific construct Additionally few
data are available regarding the relations between liking
and wanting and hunger and satiation Epstein and
col-leagues have shown that the depravation of food can
selectively influence the willingness to work for food
[14] It has been hypothesized that the physiological
state of hunger can influence desire to eat [19], but it
also has been reported that subjective food liking
oper-ates independently of perceived hunger [20]
The Eating Environment & Portion Size
The effect of large portions on food intake is well
researched The influence and change in portion sizes
over the past three decades have been suggested to
sig-nificantly contribute to the obesity epidemic [21]
Por-tion sizes have increased in a near parallel rate to the
rise in obesity [22] and increases in portion sizes have
been shown to markedly increase food and energy
intake in both children [23,24] and adults [5,25,26],
although only few studies have reported a direct
rela-tionship between portions of food and BMI [7,27,28]
Currently there is a gap in the literature regarding the
mechanisms by which portion size impacts intake We
previously theorized that the initial amount of food
pre-sented could impact food intake based on reports that
removing the visual cue of food after seeing the meal
(via blindfolding) did not attenuate the portion size
effect [7] To date, few studies have directly assessed
food appeal and desire to eat of a variety of foods varied
by portion size without the confound effects of satiety
Study Aims and Hypotheses
This study aimed to assess the reliability of a computer paradigm and image set that could be easily dissemi-nated to investigate individuals’ characteristics and simi-larities and differences between food appeal and desire
to eat In addition, we aimed to examine the relation-ships among food appeal ratings and ratings of desire to eat, food categories, portion size, energy density, and participant characteristics Our primary hypotheses included: 1) food appeal and desire to eat would be positively correlated, but individuals would differentiate between these two constructs, specifically desire to eat would be rated lower by nature of the controlled full energy state of the participants (see methods); 2) when separating food images by category, discretionary foods (desserts, energy dense foods) would be rated highest in both food appeal and desire to eat; 3) BMI, hunger and dietary disinhibition would be positively associated with desire and appeal ratings, whereas fullness and dietary restraint would have inverse relations with desire and appeal ratings; 4) individuals would rate large portions
of food higher for appeal and desire; and 5) energy den-sity of food would be positively associated with food appeal and desire to eat ratings
Methods
Image Set Development
Over 600 images of food were considered for inclusion into the set including those: 1) taken by lab personnel; 2) obtained via the internet; 3) from the International Affective Picture System [29]; 4) and used in previous fMRI research [30,31] Permission was obtained to use images downloaded from the internet and from previous research All images were matched for brightness and contrast using Microsoft Office Picture Manager® (Microsoft, Seattle WA, 2007), were sized to be at least
800 × 600 pixels and were converted to a JPEG file type After the images were standardized, images were excluded if: the image quality (clarity, brightness, con-trast) was poor or the food could not be easily identi-fied; if there was an overrepresentation of a kind of food item; or if the food was presented in a manner not typi-cal for consumption (e.g., a whole, uncut pineapple) Liquids were excluded from the image set due to the difficulty in identifying the liquid Images were selected
to represent a variety of ethnic foods and food cate-gories as well as different portion sizes
Food images were assigned to categories similar to food groups presented in the Health and Human Ser-vices 2005 Dietary Guidelines for Americans [32] When
a mixed plate of food was shown, the category assigned
Trang 3represented the predominant food item in the image, as
determined by five members of the research staff If
there was no predominant food, the image was placed
into a“mixed dish” category Examples of foods
repre-sented in each category and the number of images in
each category can be seen in Table 1
A total 165 food images were presented to each
parti-cipant in a random order This included 104 unique
food images, 46 images of foods which varied by portion
size (23 food pairs) and 15 repeated images for reliability
analyses
The 46 portion size images were all photographed by
research staff Twenty-three foods were presented in a
small portion (based on one serving per manufacturer
nutritional facts label or USDA guidelines) and a large
portion (double the small portion) Each of the portion
size images was photographed with identical
presenta-tion on the same plate in the same lighting The angle
and distance from which these images were taken were
based on how an average height male (5’ 10”) would see
a food if seated at a table These techniques were used
to ensure the scale of the foods included in the portion
size images consistent and apparent
For reliability analyses, five sets of 15 images were
randomly selected from the original 150 One of the five
sets was imbedded randomly into the original set of 150
images for each participant Thus, each participant rated
a total of 165 images in their session Across the entire
sample of participants, reliability data was collected on a
total of 75 different images (5 sets of 15 images)
Relia-bility was not assessed on all 150 images to minimize
participant burden
ImageRate Computer Paradigm
The computer program ImageRate was written in
Visual Basic for Applications (Microsoft, Seattle WA,
2007) and Microsoft Office Access®(Microsoft, Seattle
WA, 2007) was used as user interface and data storage
The images were presented to the participant one at a
time in a random order on a 17 inch (176 cm) moni-tor Ratings were assessed for each image by visual analog scales (VAS; 0-100) measuring food appeal and desire to eat the food presented in the image The question measuring food appeal was phrased ‘How appealing is this food?’ anchored by ‘Not appealing at all’ to ‘Extremely appealing.’ Appeal was defined as the amount the person liked the presented food item The question to measuring desire to eat was phrased,‘How much do you desire to eat this food?’ anchored by ‘I have no desire to eat this food’ to ‘I have a strong desire to eat this food.’ Desire to eat was specifically defined as the drive to consume some of the presented food at that point in time The VAS were presented under the image of the food one at a time and partici-pants progressed through the images and questions at their own pace
Measures & Procedures
A total of 130 individuals (M = 56, F = 74) completed the study One woman was excluded from analysis due
to an outlying BMI (62.4) This participant’s BMI was four SD above the mean and a Cook’s Distance greater than 1 revealed that her BMI was an overly influential data point All subsequent analyses are presented on the remaining 129 participants Seventy-four participants (M
= 27, F = 47) were classified as lean (BMI 21.6 ± 1.9) and 55 participants (M = 29, F = 26) were classified as overweight (BMI 31.7 ± 6.8) Demographic information and participant characteristics are presented in Table 2 Participants were recruited via flyer, email distribution lists and website message boards regarding a study investigating‘opinions about food’ in the Denver Metro and Northern Colorado areas No further information regarding the purpose of the study was given Indivi-duals were excluded if they had a visual disability that would affect the ability to differentiate colors or impair seeing in the dark or any developmental disability that could impact data collection
Table 1 Descriptive information of the food images and categories selected for the ImageRate program
Number of Images Included
Examples of Foods in Each Category Fruit 18 Strawberries, ready to eat oranges and mixed fruit platters
Discretionary
foods
21 Brownies, ice cream, cakes and high calorie savory foods such as French fries, and potato chips.
Vegetables 15 Broccoli, baked potatoes, peas and mixed vegetable dishes (e.g., salad or salsa)
Mixed dishes 28 A plate with eggs and hash browns, a basket of fish and chips and pizza with meat and vegetable
toppings
Trang 4Each participant attended one session conducted
either at the University of Colorado -Denver or
Color-ado State University Prior to the session participants
were asked to adhere to their normal eating habits,
upon arrival, once informed consent was reviewed and
obtained, participants were first asked to drink≥ 80% of
a Boost®nutritional drink (Nestlé HealthCare Nutrition,
Fremont, MI 2008) to control for individuals’ hunger/
fullness levels across the sample The nutritional drink
contained 240 kcal, 10 grams of protein and 4 grams of
fat A gap of 15 minutes was placed between
consump-tion of the nutriconsump-tional drink and ratings to allow for the
satiating effect of the supplement to occur Participants
were then asked to fill out VAS for hunger and fullness
(0-100; ranging from not hungry/full at all to extremely
hungry/full) prior to the ImageRate procedure
The participant was given instructions on how to use
the ImageRate program and given the opportunity to
practice with the assistance of the researcher to ensure
complete understanding of the procedures All ratings
were completed on the same 17 inch (176 cm)
compu-ter monitor in a quiet, dimly lit, private room Once the
image rating was finished, the participant then
com-pleted the Three Factor Eating Questionnaire (TFEQ)
[33] The TFEQ assesses dietary behaviors designed to
produce weight loss or maintenance, monitoring of
body shape, and importance of thinness (sample item: I
count calories as a conscious means of controlling my
weight) This scale has shown internal consistency (a’s
ranged from 85 to 93) and temporal reliability;
1-month test-retest r = 98 [33,34] Constructs of interest
for this investigation were dietary restraint (range 0-21)
and dietary disinhibition (range 0-16) At the end of the
session, the participant’s height and weight were
mea-sured with a standardized scale and stadiometer All
procedures and measures were approved by the
Color-ado Multiple Institutional Review Board
Statistical Analyses
Statistical analyses were performed using SAS Version 9.1 (SAS Institute Inc, Cary, NC 2003) All tests were two-sided, with the significance level set at p < 0.05 Data are presented as mean ± standard deviation (SD) unless otherwise specified Descriptive statistics were performed on all data including means, SD, standard error of the means (SEM) and weight status Weight sta-tus was determined by calculating body mass index (BMI; kg/m2) and then BMIs were dichotomized into lean (BMI < 25) and overweight (BMI ≥ 25) groups Independent measures t-tests were used to compare participant characteristics by weight status and sex Appeal and desire were analyzed using repeated mea-sures t-tests to study differences in ratings among food categories, and food appeal and desire to eat for each food category Pearson correlations were used to analyze the relationships among appeal and desire by food cate-gory and participant characteristics Participant charac-teristics of interest included: BMI, hunger, fullness and dietary restraint and disinhibition To study the effect of portion size on appeal and desire ratings, difference scores were calculated between ratings for the large and small portions Previous reports suggest differential responses to portion size by sex and weight status [35]
To account for this, weight status, sex, level of fullness and interactions where included in the repeated mea-sures analyses of variance model when testing the effect
of portion size on ratings In the case of a significant interaction, least squared means were compared using a Tukey-Kramer adjustment for multiple comparisons (p
< 0.05) The USDA Food Database was used for the dietary analyses of the energy (kcal/food (g)) Pearson correlational analyses were used to study the relation-ship between appeal and desire ratings and energy den-sity Pearson correlations and Cronbach’s a were calculated to assess test/retest reliability utilizing the repeated images that were imbedded into the image set
Results
Food Appeal & Desire to Eat Ratings
The overall mean ratings for appeal and desire are pre-sented in Table 3 Food appeal was significantly higher than desire to eat (57.9 ± 11.6 v 44.7 ± 18.0; t = 3.14; p
< 0.05; Table 3), yet appeal and desire were positively correlated (r = 0.57, p < 0.001) When examining at the food categories, fruit had a mean appeal rating of 71.8, which was significantly higher than all other food cate-gories (ratings ranged from 49.3 - 61.7) A similar pat-tern was observed in desire (Table 3)
BMI was positively associated with ratings for desire
to eat, but not food appeal (Table 4) When examining the relationship between weight status and ratings by food category, BMI was the only significant correlate of
Table 2 Sample description and characteristics
Age (y) 34.5 (11.2) 33.3 (11.3) 33.8 (11.5)
BMI 26.0 (5.5) 25.7 (7.8) 25.9 (6.8)
Education (y) 16.1 (1.2) a 15.5 (1.7) b 15.7 (1.5)
Dietary Restraint # 8.1 (4.5) 9.0 (4.5) 8.6 (4.5)
Dietary Disinhibition# 5.3 (3.3) 6.4 (3.7) 5.9 (3.6)
Hunger 35.0 (23.3)a 25.2 (21.3)b 29.5 (22.6
Fullness 45.6 (23.9)a 59.0 (22.1)b 53.2 (23.7)
Values are presented in mean (SD)
a, b
Different superscripts indicate significant differences between men and
women p < 0.05
#
Measured via the Three Factor Eating Questionnaire [33] Scale ranges:
restraint (0 - low reported restraint, 21 - high dietary restraint); disinhibition (0
- low reported disinhibition, 16 -high reported disinhibition)
Trang 5appeal ratings for discretionary foods (Table 4) The
relationship between BMI and desire to eat discretionary
foods was driven by overweight individuals in that BMI
was correlated with desire to eat discretionary foods in
overweight (r = 0.38, p < 0.01), but not lean individuals
Desire to eat discretionary foods, grains, vegetables, and
protein all had similar correlation with BMI, followed
closely by trending relationship with mixed dishes and
dairy foods For ratings of desire to eat of the fruit
cate-gory was the only catecate-gory not significantly correlated
(or trending towards significance) to BMI
Hunger and fullness were associated with desire in the
directions one would anticipate: i.e., as hunger increased,
desire increased and as fullness increased, desire
decreased However, neither hunger nor fullness were
associated with food appeal (Table 4) When analyzed
by weight status, the relationship between hunger and food appeal was significant for overweight (r = 0.27, p = 0.05), but not lean individuals (p = 0.37) Analyses of appeal ratings by food categories revealed that only mixed dishes and protein were associated with hunger and fullness, whereas most food categories (except fruits and discretionary foods) were related to desire (Table 4) Reported dietary restraint was negatively correlated to desire to eat all foods, but not significantly related to food appeal, whereas disinhibition was not significantly asso-ciated with either of the ratings (Table 4) Overweight individuals reported higher restraint (9.6 ± 4.7 v 7.9 ± 4.3;
p < 0.05) and disinhibition (6.8 ± 3.9 v 5.4 ± 3.4; p < 0.05) relative to lean individuals, although these differences are clinically marginal The relationship between desire to eat and dietary restraint was significant in lean (r = -0.24, p < 0.05), but not overweight individuals When analyzed by food category, restraint was negatively associated with desire grains, vegetables, mixed dishes and protein, but was not related to fruits, discretionary foods or dairy, nota-bly both high fat food categories (Table 4) Similar to the findings with hunger and fullness, the two highest rated categories i.e., discretionary foods and fruits, were not associated with restraint Disinhibition was positively cor-related with desire to eat discretionary foods (Table 4)
Portion Size, Energy Density & Reliability
Mean difference scores (large portion rating - small por-tion rating) revealed that individuals rated large porpor-tions
Table 3 Ratings of images by food category
Food Appeal (± SD) Desire to Eat (± SD) Fruit 71.8 (12.7)* a 59.7 (19.9)* b
Discretionary foods 61.7 (14.1) a 45.9 (21.6) b
Grains 58.1 (13.9) a 44.3 (21.0) b
Dairy 49.3 (17.8) a 38.3 (21.8) b
Vegetables 56.2 (13.2) a 41.5 (19.3) b
Mixed dishes 55.2 (14.9)a 42.6 (21.6)b
Protein 53.4 (17.8)a 40.9 (23.6)b
Total 57.9 (11.6)a 44.7 (18.0)b
*indicates fruit is rated significantly higher than the other food categories (p <
0.05)
a, b
different superscripts indicate significant differences between appeal and
desire within a food category (p < 0.05)
Table 4 Pearson correlations between appeal and desire ratings by food category and participant characteristics
BMI Hunger Fullness Dietary Restraint Dietary Disinhibition Food Appeal
Desire to Eat
**p < 0.01
*p < 0.05
^
p = 0.05
Trang 6higher than small portions for both appeal, where the
large portion was rated 2.6 ± 4.4 higher than the small
portion (p < 0.001), as well as desire to eat, where the
large portion was rated 1.6 ± 3.9 higher than the small
(p < 0.001) Analysis of variance main effects of weight
status and portion size were observed for ratings of
desire to eat: overweight participants’ difference scores
were significantly higher than lean individuals’ scores for
desire to eat (2.3 ± 0.5 v 0.8 ± 0.5; p < 0.05) In
addi-tion, a significant weight status by sex interaction was
observed, specifically overweight men’s difference scores
were larger compared to lean men’s scores (2.7 ± 0.7 v
-0.3 ± 0.8; p < 0.05)
Pearson correlation analyses among scores for food
appeal, desire, and energy and sugar densities of the
foods were analyzed Appeal and desire were negatively
correlated with energy density of the foods presented in
the images (r = -0.27, p < 0.01; r = -0.27, p < 0.01
respectively)
Measures of reliability for ratings of appeal and desire
were high for both test-retest reliability and internal
consistency: food appeal (r = 0.91, Cronbach’s a = 0.95;
p < 0.001) and desire to eat (r = 0.91, Cronbach’s a =
0.95; p < 0.001)
Discussion
Food appeal and desire to eat were correlated, but their
differential relations with individual characteristics and
different overall mean ratings indicate that participants
discriminated between the two constructs despite using
the same type of metric to measure them The present
results for appeal and desire to eat dovetail previous
reports differentiating liking from wanting [17], and
wanting’s relation to weight status [19,36,37] The
con-sistency in these findings is encouraging given previous
studies used different methods (i.e., button pushing vs.,
asking desire to eat) and terms (i.e., ‘liking’ v ‘food
appeal’) This suggests these measures are capturing
aspects of the same construct and confirm the ability
for individuals to reliably differentiate between liking
and wanting However given the current lack of a gold
standard, the ability to empirically test this notion is
unavailable Results from the present study suggest that
the distinction between appeal and desire might be
moderated by weight status For example, BMI was
posi-tively related to desire, but not appeal ratings This
sug-gests that desire to eat a food item could play a larger
role in the dysregulation of weight status relative to the
food’s preference However, to date, the majority studies
evaluating liking and wanting are cross-sectional and
few involve food [17,37-39] Therefore future studies
should consider prospective designs to demonstrate the
relations between liking and wanting, habitual intake
and weight gain
We observed that BMI was positively associated with desire to eat discretionary foods, however ratings for these foods had no association with hunger or fullness This could suggest that overweight individuals’ desire to eat highly palatable foods is “overriding” homeostatic mechanisms that control food intake (i.e., satiation) These results dovetail previous theories of the develop-ment of obesity where overweight individuals’ eat for pleasure [19], consume energy dense foods in response
to hedonic hunger [40], and are highly susceptible to environmental food cues [41]
The current data demonstrate that as lean individuals’ restraint increases, their desire to eat a highly palatable food decreases Overweight individuals’ dietary restraint did not relate to their desire to eat a food, despite over-weight individuals reporting slightly higher levels of dietary restraint Notably, dietary restraint scores have been previously reported to be unrelated to measures of acute [42,43] or habitual intake [44,45] but were posi-tively related to increases in weight [46,47] and onset of binge eating and bulimia [48,49] Further, restraint has been previously reported to be positively associated with activity in reward-related brain regions when shown images of preferred foods [50] and when receiving a palatable food [51], suggesting the more restrained an individual is, the more pleasure they receive from seeing and/or consuming that food In light of these findings it has been hypothesized that overweight individuals in particular can perceive themselves as ‘restrained’, but still habitually overeat [52] Collectively, data from the present study support this notion, specifically that over-weight individuals reported being restrained eaters, but that has no effect on their desire to consume food Contrary to our hypotheses we found that the fruit category was rated higher than all other food categories
in both appeal and desire and we observed that energy density was inversely related to the ratings Individuals are born with an innate preference for sweet [53] and thus it is possible that there is inborn predisposition for the higher ratings of fruit It is also possible that the col-orful nature of fruit could be responsible for its high rating It is a possibility that fruit was rated higher than other food categories due to a response bias given fruit
is generally perceived as healthy However, if this notion held true across the food categories, one would antici-pate that vegetables would also be rated higher The sea-sonality of fruit could influence these ratings, because fruit’s appearance, taste and cost vary by the time of year However, a seasonality effect is unlikely given data collection occurred from late summer to mid-winter spanning multiple seasons
Additional analyses by food categories revealed that only the two ‘sweetest’ tasting and highest rated food categories, (discretionary foods and fruits) were not
Trang 7associated with hunger or fullness These findings
sug-gest that discretionary foods and fruits might be foods
commonly eaten outside of hunger Eating despite
feel-ing full can play a role in excess calorie consumption
and weight regulation [54-57]
Hunger and fullness were associated with desire to eat,
but not food appeal ratings This could be a result of
food appeal being a more stable trait-like characteristic
whereas desire to eat could assess a particular state at
that point in time specifically influenced by the satiating
effects of the nutritional shake consumed prior to the
ratings Because participants were feeling full, they
might want to consume a food less, but that food item
is still appealing Because fullness is a transient state
and the participants were asked to rate their desire at
that point in time, we suggest that individual’s
inter-preted desire to eat as an immediate sensation (e.g.,“I
want this food right now”), whereas appeal was more of
a generalized, stable feeling Finlayson and colleagues
reported differences in liking and wanting ratings when
individuals were in differing energy states [16,17]
Therefore, we hypothesize that if our study were
repli-cated in the fasted state, ratings for desire to eat would
be more similar to food appeal This hypothesis raises
the question of whether appeal and desire originate in
the same manner Preference (similar to food appeal) is
developed, in large part, via repeated exposure and
phy-siological learning [58,59], but it is unclear how
indivi-duals develop desire (or wanting)
It is important to acknowledge limitations in the
pre-sent investigation First, there are multiple sensory
inputs and feedback mechanisms responsible for eating
behavior This study specifically focused on the
indivi-dual’s response to the visual food cues while
control-ling for energy state, independent of smell and taste
Because the participants’ did not actually taste the
food, the results rely on their previous experiences
with the presented foods; future studies ideally should
measure responsivity to taste However, this is a
con-siderably more challenging study design when
attempt-ing to present and taste a large number of foods,
which invoke effects of satiety Further, visual food
cues contribute to food selection and meal initiation
and thus can be thought of as anticipatory cues to
consumption Food intake and weight regulation are
complex processes and the present results should not
be over generalized Additionally, while there was
sup-port (that is, statistical significance) for our hypothesis
that overweight individuals would rate larger portions
higher than smaller portions, the effects were very
small (2-3 points; scale range 0-100) Therefore, the
public health significance and generalizability of these
results is limited While we have reported differential
effects of portion size on intake by weight status [35]
null effects have also emerged [5] Lastly, the validity
of using of VAS across group comparisons (e.g., lean
vs obese, male vs female) has been questioned [60-62] Specifically, the anchors used in VAS may denote systematically different perceived intensities to the different groups The present results using across group comparisons should be interpreted with caution and future studies should consider the use of general-ized labeled magnitude scale as described by Bartoshuk and colleagues (2004)
Conclusions
This study has resulted in a reliable computer paradigm that can assess and differentiate between food appeal and desire to eat foods using a similar metric This tool can prove useful given the ease of dissemination and flexibility in the number of foods tested without an impact on satiety Results indicate that individual and food characteristics should also be considered when assessing the appeal and desire of food images Future studies should address how these ratings relate to phy-siological measures (e.g., brain activation), food intake and longer-term weight regulation
Acknowledgements Support for this work was provided by the National Research Initiative of the USDA Cooperative State Research, Education and Extension Service, grant number # 2006-55215-16726.
Author details
1 Department of Pediatrics, Section of Nutrition, University of Colorado Denver, Aurora, CO, USA.2The Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, CO, USA 3 Division of Endocrinology, Metabolism, and Diabetes, Department of Medicine, University of Colorado Denver, Aurora, CO, USA 4 Center for Human Nutrition, University of Colorado Denver, Denver, CO, USA.
Authors ’ contributions KSB, MAC and SLJ conceived of the study and participated in its design and coordination KSB collected and analyzed the data, drafted the manuscript and was responsible for incorporating the remaining authors ’ comments SLJ assisted in the data analysis and drafting the manuscript JI participated in the design of the study, and wrote the computer paradigm ImageRate All authors provided feedback on drafts of the manuscript and read and approved the final manuscript.
Competing interests The authors declare that they have no competing interests.
Received: 21 January 2011 Accepted: 25 September 2011 Published: 25 September 2011
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doi:10.1186/1479-5868-8-101
Cite this article as: Burger et al.: Assessing food appeal and desire to
eat: the effects of portion size & energy density International Journal of
Behavioral Nutrition and Physical Activity 2011 8:101.
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